Jose Luis Castillo gained his revenge in the ring against his great Californian rival Diego Corrales in Las Vegas, knocking the World Boxing Council and World Boxing Organisation lightweight champion out in the fourth round of a dramatic fight, but only after the contest had come close to being called off over apparent attempts by the Castillo camp to cheat at the weigh-in.

The Mexican challenger had failed to make the 9st 9lb (135lb) lightweight limit, even though his personal physician Armando Barak had apparently been caught trying to place his foot under the scales to stop Castillo's true weight being registered. Barak's ploy was spotted by the astonished head of the Nevada State Athletic Commission Marc Ratner who later said: "I caught him red-footed."

Barak was immediately fined and suspended, and the commission is to launch an investigation into the incident. Castillo was also fined 10% of his fight purse, or $120,000 (£65,000), for eventually weighing in 3½lb over the lightweight championship limit, meaning the fight was not recognised as a title bout.

It was only after heated exchanges between the fighters' promoters that agreement was reached for a second weigh-in on the day of the fight, with Corrales' promoter Gary Shaw striking a deal with Bob Arum that the bout could go ahead only if both men weighed less than 10st 7lb (147lb).

Castillo made the weight, and added yet further spice to the acrimonious build-up by betting Shaw $100,000 he would knock out Corrales, who had won their first fight by stoppage five months earlier after twice being floored in the 10th round amid accusations of cheating made by the Castillo camp. Then, Castillo had claimed Corrales had bought himself extra time to recover by deliberately spitting out his gumshield before turning the course of the fight and knocking out the Mexican.

A rule amendment was made for Saturday's second contest, much to the disgust of Corrales, that the referee should make a two-point deduction if a similar thing happened again. This time, after two close and fiercely contested rounds, Castillo took command in the third when a right-hand punch staggered Corrales. Even though Corrales fought back bravely, a sweeping left hook floored him in the fourth and he was counted out by the referee Joe Cortez as he rose unsteadily after 47 seconds of the round.

"I'm happy I won the fight, but sad I couldn't make the weight. I let people down, but today was vindication," said Castillo, while Corrales said he had chosen to take the fight, even though Castillo had failed to make the championship weight, "because of my pride and my sport. If this [the fight] didn't happen, it would have been bad for the sport."

Shaw said he would be invoking a re-match clause in the fight contract to set up a third contest between the rivals, but expressed his disgust at the preliminary controversy: "They tried to cheat. They tried to put a foot under the scale. I question myself for allowing this fight to happen, because it was unfair to Diego Corrales."

With the cable television network Showtime anticipating impressive pay-per-view figures, and the Thomas and Mack Center completely sold out, the contest was a major commercial success. Corrales still holds the titles despite this loss, and it is certain a rubber match next year against Castillo would be another multimillion-dollar event.